The present invention relates to an apparatus for controlling an internal combustion engine, such as a gasoline engine ,using a microcomputer. More particularly, the invention relates to an engine controller employing a learning control system which is adapted for use in automotive gasoline engines.
Among a variety of different kinds of internal combustion engines, gasoline engines for automobiles must be controlled over a very wide operating range with regard to their revolution speed and output under stringent emission gas regulations. It is therefore necessary to correctly maintain a required air-fuel ratio and to obtain an optimum ignition timing at all times under any operating condition.
In recent years, therefore, an engine controller has been widely employed using a microcomputer to totally determine operational conditions of the engine in order to control the air-fuel ratio and the ignition timing.
In such microcomputer-based engine controllers, a so-called learning control system has heretofore been widely used in which a variety of correction data necessary to effect an optimum-control of the engine is successively written into a memory, such as a backup RAM, and the data is used for effecting a control to improve the response speed and to compensate for a change in the characteristics caused by the aging of sensors and actuators. An example of such a learning control system is disclosed, for instance, in U.S. Pat. No. 4,593,667 filed by Hitachi, Ltd. on Mar. 19, 1985.
In such a controller using a microcomputer, on the other hand, the microcomputer may runaway at the time of an instantaneous drop in the power source voltage, such as at the time of starting of the engine. To prevent this, therefore, there has been proposed a system, as disclosed in GB Patent Laid-Open No. 2191613 filed by Hitachi, Ltd. and published on Dec. 16, 1987 in which, when a drop in the power source voltage is detected, the data in the CPU of the microcomputer is first transferred to a RAM to save it and, then, the microcomputer is reset.
In the former controller employing a learning control system, when the power source for the controller is abnormally interrupted, the data stored in the memory becomes no longer reliable at that moment due to the occurrence of erroneous writing by the microcomputer. By taking this fact into consideration in the above-mentioned prior art, therefore, in case the power source is abnormally interrupted, the data for learning control is all initialized, i.e., the data stored in the memory, such as a backup RAM, is all initialized immediately after the power source has recovered.
Here, in such a system, it is desired that the microcomputer is reset like in the latter one of the aforementioned prior arts.
However, in the latter prior art, which responds to a drop in the power source voltage by retaining the data and then resetting the microcomputer, is employed in an engine controller having a learning control function as mentioned above, even a drop in the power source voltage caused under a normal condition of the engine, such as at the time of engine starting, is erroneously recognized as an abnormal operation and the data for learning control is all initialized. Namely, the results of learning revert back to the initial data, and the learning effects are not sufficiently exhibited.